Benzene emissions occur during marine vessel loading operations. These emissions are.. regulated in several countries. Accordingly, we developed a one-dimensional benzene diffusion model advancing in the vertical direction within cargo tanks. Unlike other models, the model presented in this paper is based on a 1/10 scale modeling of eddy diffusion at the liquid surface during initial loading operations and advection under the tank roof during final loading operations. The model input parameters include loading rate, flow rate, cargo tank size, and temperature dependent saturated concentrations. The validity of the model is demonstrated by comparisons with onboard measurements. Other models exist. However they are based on empirical estimates, rather than rational modeling.